The present invention relates to techniques for detecting the output polarity of a disk drive read/write head, and more particularly, to a techniques for determining whether the polarity of a disk drive read/write head has reversed direction and correcting for a reversal when it occurs.
Magnetic disk drive systems include an actuator that is used to read and to write data on magnetic hard disks. An actuator moves a read/write head over the disk to read magnetic data. Magnetic data is stored on a magnetic disk in concentric data tracks. The read/write head has a write element that writes magnetic data onto the disk and a read sensor that reads magnetic data stored on the disk.
The read sensor detects positive and negative magnetic transitions on the disk and generates a linear signal that indicates these transitions. The read/write head has a polarity that effects the direction of transitions in the linear output signal. Various conditions such as high temperatures or mechanical stress can cause the polarity of a read/write head to reverse direction. When the polarity of the read/write head reverses direction, transitions in the linear output signal of the read/write head are reversed relative to the corresponding transitions on the disk. For example, positive magnetic transitions on the disk are incorrectly represented by the linear output signal as negative transitions.
Magnetic disks also contain servo sample regions. Servo information stored in the servo sample regions is used to keep the read/write head on the correct data track. The read sensor reads the servo information stored in the servo sample regions to determine if the read/write head is moving toward the inner diameter of the disk or toward the outer diameter of the disk.
The magnetic disk has a unique magnetic pattern at the beginning of the servo sample region, that is polarity sensitive, to allow the servo system to separate the servo sample region from other information on the disk. This unique pattern is known as a servo address mark. The actuator uses part of the servo information to correct movements in the read/write head that are needed to keep the read sensor on the correct data track. The actuator also uses the servo information to move the read/write head from one data track to another.
When the polarity of the read/write head reverses, the read sensor misreads the servo address mark information stored in the servo samples. When the actuator moves the read/write head based on the misread servo address mark information, it cannot keep the read/write head on the center of the data track. Instead, the read/write head may be moved in the wrong direction, and the track following or seeking system completely malfunctions. As a result, polarity reversals of the read/write head can have disastrous effects on the operation of a magnetic disk drive system.
Therefore, there is a need to detect polarity reversals of read/write heads that are used to read magnetic data and to correct for these polarity reversals.